What solution do folks use for the dreaded BFD hum? - Page 10 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #91 of 324 Old 03-23-07, 01:19 PM
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Re: What solution do folks use for the dreaded BFD hum?

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brucek wrote: View Post
If you still use any analog cable channels, I suspect there's a few hum bars in the video. The digital channels wouldn't give a hoot.....

brucek
Nope, no analog whatsoever.

Wayne - as a side note it sounds like your plan is to create a cable that goes directly from the BFD to the sub input. However if possible I'd prefer to make just an adapter piece that I can plug my existing cable into. This would provide more flexibility in the future if I move components around (not locked into a specific cable length).
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post #92 of 324 Old 03-23-07, 01:39 PM
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Re: What solution do folks use for the dreaded BFD hum?

Quote:
as a side note it sounds like your plan is to create a cable that goes directly from the BFD to the sub input
Is the ground loop not between the BFD and the source equipment? Why are you not trying this cable mod between the receiver and the BFD? This a unbalanced to balanced modification....

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post #93 of 324 Old 03-23-07, 01:58 PM
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Re: What solution do folks use for the dreaded BFD hum?

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brucek wrote: View Post
Is the ground loop not between the BFD and the source equipment? Why are you not trying this cable mod between the receiver and the BFD? This a unbalanced to balanced modification....

brucek
Good point I was thinking about this the wrong way because I was picturing modding the connecting between the BFD and the sub. When it really needs to be between the BFD and the receiver...

Which brings up a very important point. My RCA cable run from the receiver to the BFD is 25 feet and under permanently installed carpet. No way for me to switch that out. So I'll definitely need some sort of coupler/adapter that I can plug into the end of this cable (currently at the BFD) and then plug that into the BFD (replacing the connection between the receiver and BFD is not an option).
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post #94 of 324 Old 03-23-07, 02:24 PM
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Re: What solution do folks use for the dreaded BFD hum?


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lovingdvd wrote: View Post
Wayne - as a side note it sounds like your plan is to create a cable that goes directly from the BFD to the sub input.
What brucek said – you want this between the receiver and BFD. No point doing it from the BFd’s output – that won’t help.

Quote:
My RCA cable run from the receiver to the BFD is 25 feet and under permanently installed carpet. No way for me to switch that out. So I'll definitely need some sort of coupler/adapter that I can plug into the end of this cable
I don’t know of any decent female RCA connectors, so I’d just make a short cable with a male RCA and an XLR (or 1/ 4” TRS), and use a coupler to connect that to the cable you’re using now.

Quote:
So Wayne if you'd be so kind as perhaps to provide some detailed instructions
Basically, all you need to do is connect the RCA’s center conductor (signal +) to the XLR’s Pin 2 terminal, and the RCA’s shield (-) to the XLR’s Pin 3. Using a TRS, it would be (+) to tip, and (-) to ring. See the bottom diagram here, only the black wire would go to Pin 3. Do not add the jumper between Pins 1 and 3

If you need more detailed instructions, let me know.

Regards,
Wayne



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post #95 of 324 Old 03-23-07, 02:50 PM
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Re: What solution do folks use for the dreaded BFD hum?

OK - I'm confused already!

I'm not sure what the difference is between XLR vs. TRS and how/if it matters which to use.

Currently my RCA line from the receiver goes into a Radio Shack plug that has the 1/4" pin on one end and the RCA female on the other. Is this a XLR, TRS, or neither?

Also in my custom cable thingie what is going to serve as the female end that my existing RCA feed from the receiver will now go into?

I'm also confused about that bottom diagram you reference in that link. That link shows a XLR but when talking about using a TRS you refer to it even though it is a XLR.

I'm also confused about this custom piece of cable. It sounds like a need to by a RCA cable with a female end on one end that my existing RCA would feed into, then cut off the other end and solder that into the XLR / TRS?

If its not too much trouble can you provide the short list of Radio Shack part #s I'll need, and exactly what wires I'll be connecting to what terminal # in each part #? Think of it as a "anti-hum custom cable creation for dummies guide"

Once I know what to get I'll pick up the parts on my way home today and give it a shot, and let you know how it works out! Thanks again!!
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post #96 of 324 Old 03-23-07, 10:45 PM
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Re: What solution do folks use for the dreaded BFD hum?


Quote:
I'm not sure what the difference is between XLR vs. TRS and how/if it matters which to use.
It doesn’t matter which you use:

TRS (tip/ring/sleeve, aka “stereo plug”)



XLR male (input)



XLR female (output)


Quote:
Currently my RCA line from the receiver goes into a Radio Shack plug that has the 1/4" pin on one end and the RCA female on the other. Is this a XLR, TRS, or neither?
That would be a TS (tip/sleeve, aka “mono plug”).

Quote:
I'm also confused about that bottom diagram you reference in that link. That link shows a XLR but when talking about using a TRS you refer to it even though it is a XLR.
When I said “or TRS” that meant a different connector, not a different name for an XLR. Either connector can be used for a balanced input. See Pg. 19 of the BFD manual for some details.

Quote:
I'm also confused about this custom piece of cable. It sounds like a need to by a RCA cable with a female end on one end that my existing RCA would feed into, then cut off the other end and solder that into the XLR / TRS?
You could certainly do that.

Quote:
If its not too much trouble can you provide the short list of Radio Shack part #s I'll need,
Are you going to make it from scratch, or chop one end off a re-made cable and solder on an XLR? Different parts list for each...

Regards,
Wayne



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post #97 of 324 Old 03-23-07, 11:40 PM
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Re: What solution do folks use for the dreaded BFD hum?

Hi Wayne - thanks for all the great feedback.

Probably the most straight forward thing to do would be to cut off the end of the 25 foot RCA at the BFD of that comes from the receiver and change that into the gizmo stero plug.

HOWEVER - I'm not comfortable doing that for a couple reasons. Mainly because that is an impossible cable to rerun and if I mess it up I'm stuck. In addition, if I should change my set up later and no longer use the BFD then I have a stereo plug on one end of a cable that I likely need to be RCA (aka the way it was).

So.... here's what I'd like to do that is the safest approach I think and one that I'd be most comfortable with. I'd like to construct a new cable that is hard wired on one end into a 1/4" TRS that will go into the BFD input, and on the other end has a female RCA plug. This way I can put this gizmo inline without any disruption to my existing 25 foot cable.

Just doing a quick search at Radio Shack it looks like there is no RCA female cable that's just a cable, but plenty of ones that are part of a Y adapter. I assume I can just buy one of those and cut off one of the female ends with some cord to spare. Then tie that somehow into the TRS with a basic wiring configuration? Also please clarify if the 1/4" plug is supposed to be mono or stereo (TRS vs. a TS). I mention this because you say I use a TS now but it sounds like part of this plan involves going to a TRS.

Thanks again!!
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post #98 of 324 Old 03-24-07, 03:07 AM
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Re: What solution do folks use for the dreaded BFD hum?

To clarify my comments on the cable grounding...and this applies to everyone and any system...

You should verify that there is a GOOD ground on the incoming lines such as cable, sat, antenna, etc. This means measure the resistance (with the equipment disconnected) between the cable ground and the a.c. ground. If it is more than a few ohms, it may be the source of the problem and it definitely needs to be addressed from a protection point of view. I do not recommend using isolation transformers as they may introduce problems with low frequency communication needed for digital and broadband cable. They should ALWAYS be after ground points and surge suppression in the line and just before the receiving equipment if they are used.

The BFD hum problem usually comes down to one of two problems, poor or different ground paths such as on a poorly grounded cable line or simply improper matching of the balanced/unbalanced equipment. Ultimately a decent matching transformer may be needed.

I have tested the radio shack transformer, btw, and find no problem with its low frequency performance. The problem is that the combination of connectors requires a clumsy 6 inch kludge.




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post #99 of 324 Old 03-24-07, 08:57 AM
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My current plan...

OK, so after reading through this a few more times it started to sink in and actually now seems pretty simple.

Here is my current plan:

- I've decided to use a TRS instead of a XLR. The XLR actually looks a bit easier to work with. However, Radio Shack apparently does not sell a MALE XLR plug, which is need to feed the input of the BFD. Please correct me if I'm wrong.

- First I'll need a female RCA plug to accept the sub out line coming from my receiver. Radio Shack apparently doesn't sell the adapter alone. So I'm going to purchase a cable like this one http://www.radioshack.com/product/in...tId=2103367&cp (catalog # 42-2542) and cut off one of the ends leaving about 6" of cord on it to work with.

- Next I'm going to purchase this TRS 1/4" plug http://www.radioshack.com/product/in...tId=2103445&cp (catalog #274-139)

- Next per Wayne's earlier instructions I'm going to connect the RCA’s center conductor (signal +) to the tip of the TRS, and the RCA’s shield (-) to the ring of the TRS.

- Plug her in, and hope for the best!

My only remaining questions are:

1) Does the above look like a good plan (make sense)?

2) Once I cut off the RCA female part from the Radio Shack plug, will it be obvious which lead is the signal + and which is the shield - ? If not, I guess I can easily confirm this with an ohm meter.

3) Regarding the TRS plug - I've never worked with one of these. What do you do - unscrew the pin from the case to get at the solder joints? And the biggest question of them all, within the TRS solder joints are they labeled so I know which are the ring, tip and shield? If not what is the procedure with an ohm meter to determine this (I don't know when looking at the plug which is shield and which is ring - tip is fairly obvious! )

Thanks all!
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post #100 of 324 Old 03-24-07, 09:57 AM
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Re: What solution do folks use for the dreaded BFD hum?



Quote:
Just doing a quick search at Radio Shack it looks like there is no RCA female cable that's just a cable, but plenty of ones that are part of a Y adapter. I assume I can just buy one of those and cut off one of the female ends with some cord to spare. Then tie that somehow into the TRS with a basic wiring configuration?
That’ll work. Only we’re hopefully going to solder and not “tie?”

Quote:
Also please clarify if the 1/4" plug is supposed to be mono or stereo (TRS vs. a TS). I mention this because you say I use a TS now but it sounds like part of this plan involves going to a TRS.
Yes, we’re going to use the stereo plug instead of the mono plug you’re using now.

Quote:
However, Radio Shack apparently does not sell a MALE XLR plug, which is need to feed the input of the BFD. Please correct me if I'm wrong.
It’s doubtful that Radio Shack sells any loose XLRs. However, if you have a guitar shop somewhere in town, they probably do.

Quote:
- Next I'm going to purchase this TRS 1/4" plug http://www.radioshack.com/product/in...tId=2103445&cp (catalog #274-139)
That’ll work, although I’d prefer to see one with a metal barrel. Just don’t step on the thing!

Quote:
2) Once I cut off the RCA female part from the Radio Shack plug, will it be obvious which lead is the signal + and which is the shield - ? If not, I guess I can easily confirm this with an ohm meter.
The shield is signal (-), the center conductor is signal (+). The shield is what’s wrapped around the center conductor. It’ll look something like this (the braided part is the shield):





Quote:
And the biggest question of them all, within the TRS solder joints are they labeled so I know which are the ring, tip and shield?
The shield is easy. The tip and ring you’ll have to check with an ohm meter.

Again, look at the picture on Pg. 19 in the BFD manual (Fig. 10).

Regards,
Wayne



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